Collars are placed around the necks of animals for various reasons, such as to attach an electronic device to an animal for purposes of tracking it. However, with wild animals who are not in frequent contact with humans, it is not safe to use a fixed length collar, particularly with young animals, since if the animal grows significantly such that the circumference of its neck increases, the animal would eventually be strangled as a result of the fixed length collar. An elastic material may be used, but such collars continually exert force on the animal's neck, which force may get larger as the animal grows, and may be damaging to the animal.
Expandable collars have been disclosed. These employ loops of collar material with each loop closed by a weak link so that when sufficient force is applied one of the the links breaks and the collar circumference expands by the amount of material that is in the loop. Such collars are available, for example, from Telonics, Inc. While these types of collars support a limited amount of expansion, they cannot contract. This may cause problems, for example, when an animal loses a significant amount of weight, such as due to sickness or hibernation, as the collar may become very loose.